Numerical analysis of geosynthetic-reinforced embankment performance under moving loads

The performance of geosynthetic-reinforced embankments under traffic moving loads is always a hotspot in the geotechnical engineering field.A three-dimensional(3D)model of a geosynthetic-reinforced embankment without drainage consolidation was established using the finite element software ABAQUS.In this model,the traffic loads were simulated by two moving loads of rectangular pattern,and their amplitude,range,and moving speed were realized by a Fortran subroutine.The embankment fill was simulated by an equivalent linear viscoelastic model,which can reflect its viscoelasticity.The geogrid was simulated by the truss element,and the geocell was simulated by the membrane element.Infinite elements were utilized to weaken the boundary effect caused by the model geometry at the boundaries.Validation of the established numerical model was conducted by comparing the predicted deformations in the cross-section of the geosynthetic-reinforced embankment with those from the existing literature.On this basis,the dynamic stress and strain distribution in the pavement structure layer of the geosynthetic-reinforced embankment under a moving load was also analyzed.Finally,a parametric study was conducted to examine the influences of the different types of reinforcement,overload,and the moving load velocity on the geosynthetic-reinforced embankment.

Similarity quantification of soil parametric data and sites using confidence ellipses

This paper presents a confidence ellipse-based method to evaluate the similarity of soil parametric data using the database from the site investigation reports.Then,the obtained similarity assessment results of parametric data are used to further estimate the site similarity via two proposed strategies,namely the mean and weighted mean approaches.The former referred to the average of parametric data similarity degrees,while the latter was the weighted average,and the weight was calculated using the coefficient of variation(COV)of each parameter.For illustration,the liquidity index(LI)dataset was firstly used to explore the performance of the presented method in the evaluation of parametric data similarity.Subsequently,the site similarity was assessed and the effects of numbers and weights of selected parameters for study were systematically studied.Lastly,the transformation models about the relationships between Cc and x as well as between Cc and e0 were constructed to illustrate the application of the similarity analysis in reduction of transformation uncertainty.Results show that the greatest site similarity degree is at about 0.76 in this study,and the maximum decrease of transformation uncertainty can reach up to 18%and 25.5%as union parametric data similarity degree increases.Moreover,the site similarity degree represents the whole similarity between two different sites,and the presented union parameter similarity degree maintains a good agreement with transformation uncertainty.

Stochastic analysis of excavation-induced wall deflection and box culvert settlement considering spatial variability of soil stiffness

In this study, a three-dimensional (3D) finite element modelling (FEM) analysis is carried out to investigate the effects of soil spatial variability on the response of retaining walls and an adjacent box culvert due to a braced excavation. The spatial variability of soil stiffness is modelled using a variogram and calibrated by high-quality experimental data. Multiple random field samples (RFSs) of soil stiffness are generated using geostatistical analysis and mapped onto a finite element mesh for stochastic analysis of excavation-induced structural responses by Monte Carlo simulation. It is found that the spatial variability of soil stiffness can be described by an exponential variogram, and the associated vertical correlation length is varied from 1.3 m to 1.6 m. It also reveals that the spatial variability of soil stiffness has a significant effect on the variations of retaining wall deflections and box culvert settlements. The ignorance of spatial variability in 3D FEM can result in an underestimation of lateral wall deflections and culvert settlements. Thus, the stochastic structural responses obtained from the 3D analysis could serve as an effective aid for probabilistic design and analysis of excavations.

Dynamic response of a pile embedded in elastic half space subjected to harmonic vertical loading

An analytical method is developed to investigate the dynamic response of a pile subjected to harmonic vertical loading.The pile is modeled as a one-dimensional（1D）elastic rod.The elastic soil is divided into a homogeneous half space underlying the base of pile and a series of infinitesimally thin layers along the vertical shaft of pile.The analytical solution for the soil-pile dynamic interaction problem is obtained by the method of Hankel transformation.The proposed solution is compared with the classical plane strain solution.Arithmetical examples are presented to demonstrate the sensitivity of the vertical impedance of the pile to relevant parameters.

Influence of the penetration of adjacent X-section cast-in-place concrete(XCC)pile on the existing XCC pile in sand

A series of small-scale 1g X-section cast-in-place concrete(XCC)pile-penetration model tests were conducted to study the effects of soil density and pile geometry on the lateral responses of an existing pile and the variations in surrounding soil stress.The results showed that the bending patterns of existing XCC piles varied with penetration depth.The lateral response of the existing pile was sensitive to the change in relative density and pile geometry.For example,the bending moment of the existing pile increased along with these parameters.The development of the radial stressσ′r/σ′v0 of the soil around an existing pile showed different trends at various depths during the penetration of the adjacent pile.Moreover,the change in radial stress during the penetration of the XCC pile did not exhibit the“h/R effect”that was observed in the free-field soil,due to the shielding effect of the existing piles.The peak value of radial stressσ′r_max/σ′v0 decreased exponentially as the radial distance r/R increased.The attenuation ofσ′r_max/σ′v0 with r/R in the loose sand was faster than in the medium-dense or dense sands.Theσ′r_max/σ′v0 at the same soil location increased with the cross-section geometry parameter.

Seismic behaviors of utility tunnel-soil system: With and without joint connections

Seismic responses of utility tunnel-soil system were studied via shaking table model tests with considerations of two kinds of double box utility tunnels:with and without joint connections.These two testing utility tunnel models were made of galvanized iron wire and micro-concrete,and the ground was simulated by the dry standard sand through layered tamping treatment.The utility tunnel-soil system was subjected to horizontal vibration in uniaxial direction perpendicular to the longitudinal direction of tunnel model.Via instrumentations of earth pressure gauges,accelerometers and strain gauges,the earth pressure response,acceleration response and bending moment response were measured.The testing results show that the joint connections in the utility tunnel along the longitudinal direction play an important role in determining the characteristic of earth pressure response and bending moment response,whereas the effect of joint connections on acceleration response is less significant.In addition,the partition wall exhibits the consistent acceleration response with the side-wall of double box utility tunnel model under seismic condition.Based on the testing results,it is suggested that the joint connection should be taken reasonably into consideration during design and construction for engineering practice.

Numerical analysis of seismic response of rectangular underground structure in coral sand

The underground structure in coral sand is threatened by earthquake.The special dynamic characteristics of coral sand were realized by finite difference program.Specifically,the stress–strain loops,shear modulus attenuation and hysteresis behaviour of coral sand were simulated using hysteresis damping.On this basis,numerical models were established to study the seismic response of the rectangular underground structure in coral sand,and the fluid–solid coupling and soil-structure interaction were considered.The results illustrate that the increasing relative density of coral sand foundation reduces the excess pore water pressure(EPWP),but amplifies the horizontal dynamic soil pressure of the coral sand-underground structure system.The increase in the permeability coefficient of coral sand reduces the EPWP accumulation,which leads to an increase of the stiffness and a decrease of the acceleration amplification of coral sand sites.

Propagation characteristics of transient waves in low-strain integrity testing on cast-in-situ concrete thin-wall pipe piles

The three-dimensional effects of pile head and the applicability of plane-section assumption are main problems in low-strain dynamic tests on cast-in-situ concrete thin-wall pipe piles.The velocity and displacement responses were calculated by a theoretical formula deduced by the authors.The frequency and influencing factor of high-frequency interference were analyzed.A numerical method was established to calculate the peak value and arrival time of incoming waves on top of the piles.The regularity along circumferential and the influence of radius or impulse width were studied.The applicability of plane-section assumption was investigated by comparison of velocity responses at different points in the sections at different depths.The waveform of velocity response at different points forked after the first peak,indicating that the propagation of stress waves did not well meet the plane-section assumption.

An Analytical Solution for Wave Propagation in a Pipe Pile with Multiple Defects

An analytical solution is developed in this paper to conduct the low-strain integrity testing for a pipe pile with multiple defects.The derived solution allows simulating the pipe pile as a three-dimensional model by considering the wave propagation in the vertical,circumferential and radial directions.Analytical solutions of the pile are obtained by the Laplace transform and separation of variables.Accordingly,time-domain responses of the solution are deduced by the inverse Fourier transform numerically.The solution is validated against the published solutions for an intact pile and a pile with a single defect.Parametric studies are conducted to identify and characterize the velocity responses on the top of pipe piles with multiple defects.Numerical results suggest that the reflected waves generated by the deep defects are affected by the secondary reflections from the shallow defects.A new detecting method is proposed to decrease the influence of high-frequency interferences and to predict the defective depth,which suggests putting the receiver at the point of 90°along the circumferential direction.

Review of transparent soil model testing technique for underground construction:Ground visualization and result digitalization

In geotechnical engineering,the transparent soil(also called transparent media)technique is an effective tool for conducting experimental tests and investigating the displacement characteristics and stress distribution of soils.It plays a vital role in the observation of internal soil deformations.This study aims to briefly review the current state of some of the common materials used to formulate transparent soil models and the application of the transparent soil technique to underground construction over the last 20 years.To this end,the basic concepts of transparent soils are introduced.Then,several representative applications of transparent soil in underground construction(i.e.,soil deformations induced by the penetration of pile foundations,tunnel excavation-induced movements,and structural responses caused by braced excavations)are presented.Because some research gaps may exist,certain potential research topics are proposed.This review can serve as a guideline for researchers performing experiments using transparent soils.